Method for receiving nrs and nb-iot device thereof

ABSTRACT

One disclosure of the present specification proposes a method for receiving a Narrowband Reference Signal (NRS) by a Narrow band Internet of Things (NB-IoT) device. The method may comprise receiving the NRS on at least one or more orthogonal frequency division multiplexing (OFDM) symbols. The one or more OFDM symbols are in a time division duplex (TDD) subframe. If the TDD subframe corresponds to a TDD special subframe, the one or more OFDM symbols for receiving the NRS is determined based on which TDD special subframe configuration index among a plurality of TDD special configuration indexes is used by the TDD special subframe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/535,551, filed on Aug. 8, 2019, which is a continuation of U.S.application Ser. No. 16/249,569, filed on Jan. 16, 2019, now U.S. Pat.No. 10,425,265, which is a continuation pursuant to 35 U.S.C. § 119(e)of International Application No. PCT/KR2018/007770, filed on Jul. 10,2018, which claims the benefit of U.S. Provisional Applications No.62/531,363 filed on Jul. 12, 2017, No. 62/674,562 filed on May 21, 2018,and Korean Patent Application No. 10-2018-0038747 filed on Apr. 3, 2018,the contents of which are all hereby incorporated by reference herein intheir entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to mobile communication.

Related Art

In recent years, communication, i.e., machine type communication (MTC),occurring between devices or between a device and a server without ahuman interaction, i.e., a human intervention, is actively underresearch. The MTC refers to the concept of communication based on anexisting wireless communication network used by a machine device insteadof a user equipment (UE) used by a user. Meanwhile, since the existingLTE system has been designed for the purpose of supporting high-speeddata communication, it has been regarded as an expensive communicationmethod. However, the MTC may be widely used only when a price is lowaccording to a characteristic thereof. Therefore, a method of reducing abandwidth for MTC to be smaller than a system bandwidth has beenexamined for cost reduction.

Also, the MTC is recently getting attention as a means to implementInternet of Things (IoT).

As one solution to provide IoT devices at low cost, an operation schemefor IoT devices is under consideration, which makes an IoT deviceoperate with bandwidth more reduced than the system bandwidth of a cell.

As described above, IoT communication operating with reduced bandwidthis called Narrow Band (NB)-IoT communication.

To improve channel estimation and decoding performance of an NB-IoTdevice, Narrowband Reference Signal (NRS) has been proposed.

However, up to now, research has been conducted only into transmissionof the NRS from frequency division duplex (FDD)-based subframes, andresearch into a method for transmitting the NRS on a time divisionduplex-based subframe has not been conducted yet.

SUMMARY OF THE INVENTION

Accordingly, a disclosure of the present specification has been made inan effort to solve the aforementioned problem.

To achieve the aforementioned purpose, a disclosure of the presentspecification provides a method for receiving a narrowband referencesignal (NRS). The method may be performed by a narrowband internet ofthings (NB-IoT) device and comprise: receiving the NRS on at least oneor more orthogonal frequency division multiplexing (OFDM) symbols. Theone or more OFDM symbols may be in a time division duplex (TDD)subframe. If the TDD subframe corresponds to a TDD special subframe, theone or more OFDM symbols for receiving the NRS may be determined basedon which a TDD special subframe configuration index, among a pluralityof TDD special subframe configuration indexes, the TDD special subframeuses.

The TDD special subframe including the one or more OFDM symbols forreceiving the NRS may use at least one of TDD special configurationindexes 1, 2, 3, 4, 6, 7, 8 and 9.

The one or more OFDM symbols for receiving the NRS may include at leastone of 6th and 7th symbols in the TDD special subframe.

The NRS may not be received on at least one TDD special subframe usingTDD special configuration indexes 0 and 5.

The one or more OFDM symbols for receiving the NRS may include at leastone of 2nd and 3rd symbols in the TDD special subframe.

The NRS on the TDD special subframe may be generated based on a normaldownlink subframe.

The method may comprise: receiving a second reference signal (RS) in aTDD special subframe using a TDD special subframe configuration index10.

The second RS may include a cell-specific reference signal (CRS) if aNB-IoT operation mode is an inband-same PCI mode representing an inbandsame physical cell identifier (PCI).

If the NB-IoT operation mode is the inband-same PCI representing theinband same PCI, a location of a resource element (RE) to which the NRSis mapped may be different from a location of a RE to which the CRS ismapped.

The second RS may include an NRS if a NB-IoT operation mode is aninband-different PCI mode representing an inband different PCI.

If the NB-IoT operation mode is the inband-different PCI representingthe inband different PCI, an RE to which the CRS is to be mapped may beused as a blank RE.

The special subframe using the TDD special subframe configuration index10 may be designated as a valid subframe.

The special subframe using the TDD special subframe configuration index10 may include a downlink pilot time slot (DwPTS) in which a downlinkdata is to be received.

The TDD special subframe in which the NRS is received may be a validsubframe in which a downlink data is to be received.

To achieve the aforementioned purpose, a disclosure of the presentspecification provides a narrowband internet of things (NB-IoT) devicefor receiving a narrowband reference signal (NRS). The NB-IoT device maycomprise: a transceiver; and a processor configured to receive, via thetransceiver, the NRS on at least one or more orthogonal frequencydivision multiplexing (OFDM) symbols. The one or more OFDM symbols maybe in a time division duplex (TDD) subframe. If the TDD subframecorresponds to a TDD special subframe, the one or more OFDM symbols forreceiving the NRS may be determined based on which a TDD specialsubframe configuration index, among a plurality of TDD special subframeconfiguration indexes, the TDD special subframe uses.

According to the disclosure of the present invention, the problem of theconventional technology described above may be solved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a wireless communication system.

FIG. 2 illustrates a structure of a radio frame according to FDD in 3GPPLTE.

FIG. 3 illustrates a structure of a downlink radio frame according toTDD in the 3GPP LTE.

FIG. 4a illustrates one example of Internet of Things (IoT)communication.

FIG. 4b illustrates cell coverage extension or enhancement for IoTdevices.

FIG. 4c illustrates one example of transmitting a bundle of downlinkchannels.

FIGS. 5a and 5b illustrate an example of a sub-band in which IoT devicesoperate.

FIG. 6 illustrates an example where time resources that may be used forNB-IoT are represented in units of M-frames.

FIG. 7 is another example illustrating time resources and frequencyresources that may be used for NB IoT.

FIG. 8 illustrates an example of subframe type in the NR.

FIG. 9 illustrates a third symbol of a special subframe described inSection I-1.

FIG. 10 illustrates the position of an RE to which an NRS is mappedaccording to a method of I-1-3.

FIG. 11 illustrates a symbol to which an NRS is mapped according toSection I-2.

FIG. 12 illustrates a symbol to which an NRS is mapped according toSection I-3.

FIG. 13 illustrates a block diagram of a wireless device and a basestation in which a disclosure of the present specification isimplemented.

FIG. 14 is a detailed block diagram of a transceiver of a wirelessdevice of FIG. 13.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, based on 3rd Generation Partnership Project (3GPP) longterm evolution (LTE) or 3GPP LTE-advanced (LTE-A), the present inventionwill be applied. This is just an example, and the present invention maybe applied to various wireless communication systems. Hereinafter, LTEincludes LTE and/or LTE-A.

The technical terms used herein are used to merely describe specificembodiments and should not be construed as limiting the presentinvention. Further, the technical terms used herein should be, unlessdefined otherwise, interpreted as having meanings generally understoodby those skilled in the art but not too broadly or too narrowly.Further, the technical terms used herein, which are determined not toexactly represent the spirit of the invention, should be replaced by orunderstood by such technical terms as being able to be exactlyunderstood by those skilled in the art. Further, the general terms usedherein should be interpreted in the context as defined in thedictionary, but not in an excessively narrowed manner.

The expression of the singular number in the present invention includesthe meaning of the plural number unless the meaning of the singularnumber is definitely different from that of the plural number in thecontext. In the following description, the term ‘include’ or ‘have’ mayrepresent the existence of a feature, a number, a step, an operation, acomponent, a part or the combination thereof described in the presentinvention, and may not exclude the existence or addition of anotherfeature, another number, another step, another operation, anothercomponent, another part or the combination thereof.

The terms ‘first’ and ‘second’ are used for the purpose of explanationabout various components, and the components are not limited to theterms ‘first’ and ‘second’. The terms ‘first’ and ‘second’ are only usedto distinguish one component from another component. For example, afirst component may be named as a second component without deviatingfrom the scope of the present invention.

It will be understood that when an element or layer is referred to asbeing “connected to” or “coupled to” another element or layer, it can bedirectly connected or coupled to the other element or layer orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element or layer, there are no intervening elementsor layers present.

Hereinafter, exemplary embodiments of the present invention will bedescribed in greater detail with reference to the accompanying drawings.In describing the present invention, for ease of understanding, the samereference numerals are used to denote the same components throughout thedrawings, and repetitive description on the same components will beomitted. Detailed description on well-known arts which are determined tomake the gist of the invention unclear will be omitted. The accompanyingdrawings are provided to merely make the spirit of the invention readilyunderstood, but not should be intended to be limiting of the invention.It should be understood that the spirit of the invention may be expandedto its modifications, replacements or equivalents in addition to what isshown in the drawings.

As used herein, ‘base station’ generally refers to a fixed station thatcommunicates with a wireless device and may be denoted by other termssuch as eNB (evolved-NodeB), BTS (base transceiver system), or accesspoint.

As used herein, ‘user equipment (UE)’ may be stationary or mobile, andmay be denoted by other terms such as device, wireless device, terminal,MS (mobile station), UT (user terminal), SS (subscriber station), MT(mobile terminal) and etc.

Hereinafter, based on 3rd Generation Partnership Project (3GPP) longterm evolution (LTE) or 3GPP LTE-advanced (LTE-A), the present inventionwill be applied. This is just an example, and the present invention maybe applied to various wireless communication systems. Hereinafter, LTEincludes LTE and/or LTE-A.

The technical terms used herein are used to merely describe specificembodiments and should not be construed as limiting the presentinvention. Further, the technical terms used herein should be, unlessdefined otherwise, interpreted as having meanings generally understoodby those skilled in the art but not too broadly or too narrowly.Further, the technical terms used herein, which are determined not toexactly represent the spirit of the invention, should be replaced by orunderstood by such technical terms as being able to be exactlyunderstood by those skilled in the art. Further, the general terms usedherein should be interpreted in the context as defined in thedictionary, but not in an excessively narrowed manner.

The expression of the singular number in the present invention includesthe meaning of the plural number unless the meaning of the singularnumber is definitely different from that of the plural number in thecontext. In the following description, the term ‘include’ or ‘have’ mayrepresent the existence of a feature, a number, a step, an operation, acomponent, a part or the combination thereof described in the presentinvention, and may not exclude the existence or addition of anotherfeature, another number, another step, another operation, anothercomponent, another part or the combination thereof.

The terms ‘first’ and ‘second’ are used for the purpose of explanationabout various components, and the components are not limited to theterms ‘first’ and ‘second’. The terms ‘first’ and ‘second’ are only usedto distinguish one component from another component. For example, afirst component may be named as a second component without deviatingfrom the scope of the present invention.

It will be understood that when an element or layer is referred to asbeing “connected to” or “coupled to” another element or layer, it can bedirectly connected or coupled to the other element or layer orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element or layer, there are no intervening elementsor layers present.

Hereinafter, exemplary embodiments of the present invention will bedescribed in greater detail with reference to the accompanying drawings.In describing the present invention, for ease of understanding, the samereference numerals are used to denote the same components throughout thedrawings, and repetitive description on the same components will beomitted. Detailed description on well-known arts which are determined tomake the gist of the invention unclear will be omitted. The accompanyingdrawings are provided to merely make the spirit of the invention readilyunderstood, but not should be intended to be limiting of the invention.It should be understood that the spirit of the invention may be expandedto its modifications, replacements or equivalents in addition to what isshown in the drawings.

As used herein, ‘base station’ generally refers to a fixed station thatcommunicates with a wireless device and may be denoted by other termssuch as eNB (evolved-NodeB), BTS (base transceiver system), or accesspoint.

As used herein, ‘user equipment (UE)’ may be stationary or mobile, andmay be denoted by other terms such as device, wireless device, terminal,MS (mobile station), UT (user terminal), SS (subscriber station), MT(mobile terminal) and etc.

FIG. 1 illustrates a wireless communication system.

As seen with reference to FIG. 1, the wireless communication systemincludes at least one base station (BS) 20. Each base station 20provides a communication service to specific geographical areas(generally, referred to as cells) 20 a, 20 b, and 20 c. The cell can befurther divided into a plurality of areas (sectors).

The UE generally belongs to one cell and the cell to which the UE belongis referred to as a serving cell. A base station that provides thecommunication service to the serving cell is referred to as a servingBS. Since the wireless communication system is a cellular system,another cell that neighbors to the serving cell is present. Another cellwhich neighbors to the serving cell is referred to a neighbor cell. Abase station that provides the communication service to the neighborcell is referred to as a neighbor BS. The serving cell and the neighborcell are relatively decided based on the UE.

Hereinafter, a downlink means communication from the base station 20 tothe UE1 10 and an uplink means communication from the UE 10 to the basestation 20. In the downlink, a transmitter may be a part of the basestation 20 and a receiver may be a part of the UE 10. In the uplink, thetransmitter may be a part of the UE 10 and the receiver may be a part ofthe base station 20.

Meanwhile, the wireless communication system may be generally dividedinto a frequency division duplex (FDD) type and a time division duplex(TDD) type. According to the FDD type, uplink transmission and downlinktransmission are achieved while occupying different frequency bands.According to the TDD type, the uplink transmission and the downlinktransmission are achieved at different time while occupying the samefrequency band. A channel response of the TDD type is substantiallyreciprocal. This means that a downlink channel response and an uplinkchannel response are approximately the same as each other in a givenfrequency area. Accordingly, in the TDD based wireless communicationsystem, the downlink channel response may be acquired from the uplinkchannel response. In the TDD type, since an entire frequency band istime-divided in the uplink transmission and the downlink transmission,the downlink transmission by the base station and the uplinktransmission by the terminal may not be performed simultaneously. In theTDD system in which the uplink transmission and the downlinktransmission are divided by the unit of a subframe, the uplinktransmission and the downlink transmission are performed in differentsubframes.

Hereinafter, the LTE system will be described in detail.

FIG. 2 shows a downlink radio frame structure according to FDD of 3rdgeneration partnership project (3GPP) long term evolution (LTE).

The radio frame of FIG. 2 may be found in the section 5 of 3GPP TS36.211 V10.4.0 (2011-12) “Evolved Universal Terrestrial Radio Access(E-UTRA); Physical Channels and Modulation (Release 10)”.

The radio frame includes 10 sub-frames indexed 0 to 9. One sub-frameincludes two consecutive slots. Accordingly, the radio frame includes 20slots. The time taken for one sub-frame to be transmitted is denoted TTI(transmission time interval). For example, the length of one sub-framemay be 1 ms, and the length of one slot may be 0.5 ms.

The structure of the radio frame is for exemplary purposes only, andthus the number of sub-frames included in the radio frame or the numberof slots included in the sub-frame may change variously.

One slot includes NRB resource blocks (RBs) in the frequency domain. Forexample, in the LTE system, the number of resource blocks (RBs), i.e.,NRB, may be one from 6 to 110.

The resource block is a unit of resource allocation and includes aplurality of sub-carriers in the frequency domain. For example, if oneslot includes seven OFDM symbols in the time domain and the resourceblock includes 12 sub-carriers in the frequency domain, one resourceblock may include 7×12 resource elements (REs).

The physical channels in 3GPP LTE may be classified into data channelssuch as PDSCH (physical downlink shared channel) and PUSCH (physicaluplink shared channel) and control channels such as PDCCH (physicaldownlink control channel), PCFICH (physical control format indicatorchannel), PHICH (physical hybrid-ARQ indicator channel) and PUCCH(physical uplink control channel).

The uplink channels include a PUSCH, a PUCCH, an SRS (Sounding ReferenceSignal), and a PRACH (physical random access channel).

FIG. 3 illustrates the architecture of a downlink radio frame accordingto TDD in 3GPP LTE.

For this, 3GPP TS 36.211 V10.4.0 (2011-23) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, Ch. 4 may be referenced, and this is for TDD (timedivision duplex).

Sub-frames having index #1 and index #6 are denoted special sub-frames,and include a DwPTS (Downlink Pilot Time Slot: DwPTS), a GP (GuardPeriod) and an UpPTS (Uplink Pilot Time Slot). The DwPTS is used forinitial cell search, synchronization, or channel estimation in aterminal. The UpPTS is used for channel estimation in the base stationand for establishing uplink transmission sync of the terminal. The GP isa period for removing interference that arises on uplink due to amulti-path delay of a downlink signal between uplink and downlink.

In TDD, a DL (downlink) sub-frame and a UL (Uplink) co-exist in oneradio frame. Table 1 shows an example of configuration of a radio frame.

TABLE 1 UL-DL config- Switch-point Subframe index uration periodicity 01 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms D S U U DD D D D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U D S U U D

‘D’ denotes a DL sub-frame, ‘U’ a UL sub-frame, and ‘S’ a specialsub-frame. When receiving a UL-DL configuration from the base station,the terminal may be aware of whether a sub-frame is a DL sub-frame or aUL sub-frame according to the configuration of the radio frame.

TABLE 2 Normal CP in downlink Extended CP in downlink Special UpPTSUpPTS sub- Normal Extended Normal Extended frame CP in CP in CP in CP inconfig- uration DwPTS uplink uplink DwPTS uplink uplink 0 6592*Ts2192*Ts 2560*Ts 7680*Ts 2192*Ts 2560*Ts 1 19760*Ts 20480*Ts 2 21952*Ts23040*Ts 3 24144*Ts 25600*Ts 4 26336*Ts 7680*Ts 4384*Ts 5120*ts 56592*Ts 4384*Ts 5120*ts 20480*Ts 6 19760*Ts 23040*Ts 7 21952*T — 824144*T —

<Carrier Aggregation>

A carrier aggregation system is now described.

A carrier aggregation system aggregates a plurality of componentcarriers (CCs). A meaning of an existing cell is changed according tothe above carrier aggregation. According to the carrier aggregation, acell may signify a combination of a downlink component carrier and anuplink component carrier or an independent downlink component carrier.

Further, the cell in the carrier aggregation may be classified into aprimary cell, a secondary cell, and a serving cell. The primary cellsignifies a cell operated in a primary frequency. The primary cellsignifies a cell which UE performs an initial connection establishmentprocedure or a connection reestablishment procedure or a cell indicatedas a primary cell in a handover procedure. The secondary cell signifiesa cell operating in a secondary frequency. Once the RRC connection isestablished, the secondary cell is used to provided an additional radioresource.

As described above, the carrier aggregation system may support aplurality of component carriers (CCs), that is, a plurality of servingcells unlike a single carrier system.

The carrier aggregation system may support a cross-carrier scheduling.The cross-carrier scheduling is a scheduling method capable ofperforming resource allocation of a PDSCH transmitted through othercomponent carrier through a PDCCH transmitted through a specificcomponent carrier and/or resource allocation of a PUSCH transmittedthrough other component carrier different from a component carrierbasically linked with the specific component carrier.

<Internet of Things (IoT) Communication>

In what follows, IoT will be described.

FIG. 4a illustrates one example of Internet of Things (IoT)communication.

IoT refers to exchange of information through a base station 200 amongIoT devices 100, which does not involve human interaction or exchange ofinformation through the base station 200 between an IoT device 100 and aserver 700. In this way, IoT is also called Cellular Internet of Things(CIoT) in that IoT communication employs a cellular base station.

IoT communication as described above is one type of Machine TypeCommunication (MTC). Therefore, an IoT device may also be called an MTCdevice.

IoT services may be distinguished from communication-based conventionalservices which require human intervention, including a wide range ofservices such as tracking, metering, payment, medical-care, and remotecontrol. For example, IoT services may include meter reading, levelmeasurement, use of surveillance cameras, reporting an inventory of avending machine, and so on.

Since the amount of transmission data handled by IoT communication issmall, and transmission and reception of uplink or downlink data occursinfrequently, it is preferable to lower the unit price of an IoT device100 and to reduce battery consumption according to a low data transferrate. Also, since an IoT device 100 has low mobility, channel conditionsrarely change.

FIG. 4b illustrates cell coverage extension or enhancement for IoTdevices.

Recently, cell coverage extension or enhancement of a base station toaccommodate IoT devices 100 is being considered, and various techniquesfor extending or enhancing cell coverage are under discussion.

It should be noted, however, that when cell coverage is extended orenhanced, and a base station transmits a downlink channel to an IoTdevice located in the coverage extension (CE) area or coverageenhancement (CE) area, the IoT device encounters a difficulty inreceiving the downlink channel.

To solve the problem above, a downlink channel or an uplink channel maybe transmitted repeatedly on several subframes. In this way,transmission of an uplink/downlink channel repeatedly on severalsubframes is referred to as bundle transmission.

FIG. 4c illustrates one example of transmitting a bundle of downlinkchannels.

As may be known from FIG. 4c , a base station transmits a downlinkchannel (for example, PDCCH and/or PDSCH) repeatedly to an IoT device100 located in a coverage extension area on several subframes (forexample, N subframes).

Then the IoT device or base station receives a bundle of downlink/uplinkchannels on several subframes and improves a decoding success rate bydecoding the whole or part of the bundle.

FIGS. 5a and 5b illustrate an example of a sub-band in which IoT devicesoperate.

As one solution for providing IoT devices at low cost, as shown in FIG.5a , the IoT devices may use a sub-band of, for example, approximately1.4 MHz independently of the system bandwidth of a cell.

At this time, as shown in FIG. 5a , the sub-band area in which the IoTdevices operate may be located in the central area (for example, centralsix PRBs) of the system bandwidth of the cell.

Similarly, as shown in FIG. 5b , a plurality of sub-bands for IoTdevices may be defined within one subframe for multiplexing of the IoTdevices so that the IoT devices may use separate sub-bands. At thistime, a majority of the IoT devices may use a different sub-band ratherthan the central area (for example, central six PRBs) of the systembandwidth of the cell.

As described above, the IoT communication operating with reducedbandwidth may be referred to as Narrow Band (NB) IoT communication or NBCIoT communication.

FIG. 6 illustrates an example where time resources that may be used forNB-IoT are represented in units of M-frames.

Referring to FIG. 6, a frame which may be used for NB-IoT is called anM-frame, the length of which may be 60 ms, for example. Also, a subframewhich may be used for NB IoT is called an M-subframe, the length ofwhich may be 6 ms, for example. Therefore, an M-frame may comprise 10M-subframes.

Each M-subframe may comprise two slots, and each slot may be 3 ms, forexample.

However, different from what is shown in FIG. 6, a slot which may beused for NB IoT may have a length of 2 ms, a subframe may accordinglyhave a length of 4 ms, and a frame may have a length of 40 ms. Regardingthis possibility, more details will be given with reference to FIG. 7.

FIG. 7 is another example illustrating time resources and frequencyresources that may be used for NB IoT.

Referring to FIG. 7, a physical channel or physical signal transmittedon a slot from an uplink of NB-IoT includes N_(symb) ^(UL) SC-FDMAsymbols in the time domain and N_(SC) ^(UL) subcarriers in the frequencydomain. The uplink physical channel may be divided into a NarrowbandPhysical Uplink Shared Channel (NPUSCH) and a Narrowband Physical RandomAccess Channel (NPRACH). And a physical signal in the NB-IoT may becomea Narrowband DeModulation Reference Signal (NDMRS).

The uplink bandwidths of N_(SC) ^(UL) subcarriers during T_(slot) slotsin the NB-IoT are as follows.

TABLE 3 Subcarrier spacing N_(SC) ^(UL) T_(slot) Δf = 3.75 kHz 4861440*T_(S) Δf = 15 kHz 12 15360*T_(S)

In the NB-IoT, each resource element (RE) of a resource grid may bedefined by an index pair (k,l) within a slot, where k=0, . . . , N_(SC)^(UL)−1, and l=0, . . . , N_(symb) ^(UL)−1, specifying an index in thetime and frequency domain, respectively.

In the NB-IoT, a downlink physical channel includes a NarrowbandPhysical Downlink Shared Channel (NPDSCH), Narrowband Physical BroadcastChannel (NPBCH), and Narrowband Physical Downlink Control Channel(NPDCCH). And a downlink physical signal includes a Narrowband referencesignal (NRS), Narrowband synchronization signal (NSS), and Narrowbandpositioning reference signal (NPRS). The NSS includes a Narrowbandprimary synchronization signal (NPSS) and a Narrowband secondarysynchronization signal (NSSS).

Meanwhile, NB-IoT is a communication scheme for wireless devices usingbandwidth reduced to satisfy low-complexity/low-cost constraints(namely, narrowband). The NB-IoT is aimed to allow as many wirelessdevices as possible to be connected by using the reduced bandwidth.Moreover, the NB-IoT communication is aimed to support cell coveragelarger than the cell coverage provided in the legacy LTE communication.

Meanwhile, as may be known from Table 1, when subcarrier spacing is 15kHz, a carrier having the reduced bandwidth includes only one PRB. Inother words, NB-IoT communication may be performed by using only onePRB. Here, a wireless device assumes that NPSS/NSSS/NPBCH/SIB-NB istransmitted from a base station, where a PRB connected to receive theNPSS/NSSS/NPBCH/SIB-NB may be called an anchor PRB (or anchor carrier).Meanwhile, in addition to the anchor PRB (or anchor carrier), thewireless device may receive additional PRBs from the base station. Here,among the additional PRBs, those PRBs not expected to receive theNPSS/NSSS/NPBCH/SIB-NB from the base station may be called a non-anchorPRB (or non-anchor carrier).

The NRS is generated by a sequence r_(l,ns)(m), and the sequencer_(l,ns)(m) may be mapped to a complex-valued modulation symbol, namelya_(k,l) ^((p)).

The complex-valued modulation symbol, namely a_(k,l) ^((p)) is used as areference signal for the antenna port p within a slot n_(s).

a _(k,l) ^((p)) =r _(l,n) _(s) (m′)  [Eq. 1]

k=6m+(v+v_(shift)) mod 6

l=N_(symb) ^(DL)−2, N_(symb) ^(DL)−1

m=0,1

m′=m+N_(RB) ^(max,DL)−1

The variable v and v_(shift) represent the positions in the frequencydomain with respect to other reference signals. v is determined by thefollowing equation.

$\begin{matrix}{v = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} p} = {{2000\mspace{14mu} {and}\mspace{14mu} l} = {N_{symb}^{DL} - 2}}} \\3 & {{{if}\mspace{14mu} p} = {{2000\mspace{14mu} {and}\mspace{14mu} l} = {N_{symb}^{DL} - 1}}} \\3 & {{{if}\mspace{14mu} p} = {{2001\mspace{14mu} {and}\mspace{14mu} l} = {N_{symb}^{DL} - 2}}} \\0 & {{{if}\mspace{14mu} p} = {{2001\mspace{14mu} {and}\mspace{14mu} l} = {N_{symb}^{DL} - 1}}}\end{matrix} \right.} & \left\lbrack {{Eq}.\mspace{14mu} 2} \right\rbrack\end{matrix}$

The cell-specific frequency shift is given as follows.

v _(shift) =N _(ID) ^(Ncell) mod 6.  [Eq. 3]

<Next-Generation Mobile Communication Network>

Due to the success of the long term evolution (LTE)/LTE-Advanced (LTE-A)for the fourth-generation mobile communication, a public interest in thenext-generation (so-called 5G) mobile communication is growing, andresearches into the next-generation mobile communication are conductedone after another.

The 5-th generation mobile communication, as defined by theInternational Telecommunication Union (ITU), refers to the technologyaimed to provide a data transfer speed of up to 20 Gbps and an effectivetransfer speed faster than at least 100 Mbps everywhere. The officialname of the 5-th generation mobile communication is ‘IMT-2020’, which isdue to be commercialized by 2020 worldwide.

The ITU proposed three use case scenarios: enhanced Mobile BroadBand(eMBB), massive Machine Type Communication (mMTC), Ultra Reliable andLow Latency Communication (URLLC).

URLLC is related to a use scenario which requires high reliability andlow latency. For example, such services as automated driving, factoryautomation, and augmented reality require high reliability and lowlatency (for example, latency less than 1 ms). The latency of thecurrent 4G (LTE) technology is statistically 21-43 ms (best 10%) and33-75 ms (median). This specification is not sufficient to supportservices requiring latency less than 1 ms. The eMBB described next isrelated to a use scenario requiring a mobile ultra-wideband.

In other words, the 5-th generation mobile communication system targetsto provide a capacity higher than that of the current 4G LTE, improvedensity of mobile broadband users, and support high reliability andMachine Type Communication (MTC). 5G R&Ds also target lower latency andlower battery consumption than provided by the 4G mobile communicationsystem to implement the Internet of things more efficiently. To realizethe 5G mobile communication as described above, a new radio accesstechnology (New RAT or NR) may be proposed.

In the NR, it may be taken into consideration that reception from a basestation may use downlink subframes, and transmission to the base stationmay use uplink subframes. This scheme may be applied to paired spectraand unpaired spectra. One pair of spectra indicates that two carrierspectra are involved for downlink and uplink operations. For example, inone pair of spectra, one carrier may include a downlink and uplink bandsforming a pair with each other.

FIG. 8 illustrates an example of subframe type in the NR.

The transmission time interval (TTI) shown in FIG. 8 may be called asubframe or a slot for the NR (or new RAT). The subframe (or slot) ofFIG. 8 may be used in the TDD system of NR (or new RAT) to minimize datatransfer latency. As shown in FIG. 8, a subframe (or slot) comprises 14symbols in the same way as the current subframe. The leading symbol of asubframe (or slot) may be used for DL control channel, and the trailingsymbol of the subframe (or slot) may be used for UL control channel. Theremaining symbols may be used for DL data transmission or UL datatransmission. According to the aforementioned subframe (or slot)structure, downlink transmission and uplink transmission may be carriedout sequentially in one subframe (or slot). Therefore, downlink data maybe received within the subframe (or slot), or an uplink acknowledgementresponse (ACK/NACK) may also be transmitted within the subframe (orslot). The structure of the subframe (or slot) as described above may bereferred to as a self-contained subframe (or slot). When this subframe(or slot) structure is used, time required to retransmit data which hascaused a reception error is reduced, leading to minimization of finaldata transmission waiting time. In the self-contained subframe (or slot)structure, however, a time gap may be needed for a transitioning processfrom a transmission mode to a reception more or vice versa. To this end,part of OFDM symbols employed for transitioning from DL to ULtransmission in the subframe structure may be designated as a guardperiod (GP).

<Support of Various Numerologies>

In the next-generation system, according to the advances in the wirelesscommunication technology, a plurality of numerologies may be providedfor a UE.

The numerology may be defined by the length of cyclic prefix (CP) andsubcarrier spacing. A single cell may provide a plurality ofnumerologies to a UE. If the index of numerology is represented by eachsubcarrier spacing and the corresponding CP length may be given asfollows.

TABLE 4 μ Δf = 2^(μ) · 15 [kHz] CP 0 15 Normal 1 30 Normal 2 60 Normal,Extended 3 120 Normal 4 240 Normal

In the case of normal CP, if the numerology index is represented by μ,the number of OFDM symbols per slot (N_(symb) ^(slot)), the number ofslots per frame (N_(slot) ^(frame,μ)), and the number of slots persubframe (N_(slot) ^(subframe,μ)) are given as follows.

TABLE 5 μ N_(symb) ^(slot) N_(slot) ^(frame, μ) N_(slot) ^(subframe, μ)0 14 10 1 1 14 20 2 2 14 40 4 3 14 80 8 4 14 160 16 5 14 320 32

In the case of extended CP, if the numerology index is represented by μ,the number of OFDM symbols per slot (N_(symb) ^(slot)), the number ofslots per frame (N_(slot) ^(frame,μ)), and the number of slots persubframe (N_(slot) ^(subframe,μ)) are given as follows.

TABLE 6 μ N_(symb) ^(slot) N_(slot) ^(frame, μ) N_(slot) ^(subframe, μ)2 12 40 4

Meanwhile, in the next-generation mobile communication, each symbolwithin a slot may be used as a downlink or an uplink as shown in thetable below. In the table below, the uplink is denoted by U while thedownlink is denoted by D. In the table below, X represents a symbolwhich may be used flexibly as an uplink or a downlink.

TABLE 7 Symbol number in a slot Format 0 1 2 3 4 5 6 7 8 9 10 11 12 13 0D D D D D D D D D D D D D D 1 U U U U U U U U U U U U U U 2 X X X X X XX X X X X X X X 3 D D D D D D D D D D D D D X 4 D D D D D D D D D D D DX X 5 D D D D D D D D D D D X X X 6 D D D D D D D D D D X X X X 7 D D DD D D D D D X X X X X 8 X X X X X X X X X X X X X U 9 X X X X X X X X XX X X U U 10 X U U U U U U U U U U U U U 11 X X U U U U U U U U U U U U12 X X X U U U U U U U U U U U 13 X X X X U U U U U U U U U U 14 X X X XX U U U U U U U U U 15 X X X X X X U U U U U U U U 16 D X X X X X X X XX X X X X 17 D D X X X X X X X X X X X X 18 D D D X X X X X X X X X X X19 D X X X X X X X X X X X X U 20 D D X X X X X X X X X X X U 21 D D D XX X X X X X X X X U 22 D X X X X X X X X X X X U U 23 D D X X X X X X XX X X U U 24 D D D X X X X X X X X X U U 25 D X X X X X X X X X X U U U26 D D X X X X X X X X X U U U 27 D D D X X X X X X X X U U U 28 D D D DD D D D D D D D X U 29 D D D D D D D D D D D X X U 30 D D D D D D D D DD X X X U 31 D D D D D D D D D D D X U U 32 D D D D D D D D D D X X U U33 D D D D D D D D D X X X U U 34 D X U U U U U U U U U U U U 35 D D X UU U U U U U U U U U 36 D D D X U U U U U U U U U U 37 D X X U U U U U UU U U U U 38 D D X X U U U U U U U U U U 39 D D X X X U U U U U U U U U40 D X X X U U U U U U U U U U 41 D D X X X U U U U U U U U U 42 D D D XX X U U U U U U U U 43 D D D D D D D D D X X X X U 44 D D X X X X X X XX X X U U 45 D D D D D D X X U U U U U U 46 D D D D D D X D D D D D D X47 D D D D D X X D D D D D X X 48 D D X X X X X D D X X X X X 49 D X X XX X X D X X X X X X 50 X U U U U U U X U U U U U U 51 X X U U U U U X XU U U U U 52 X X X U U U U X X X U U U U 53 X X X X U U U X X X X U U U54 D D D D D X U D D D D D X U 55 D D X U U U U D D X U U U U 56 D X U UU U U D X U U U U U 57 D D D D X X U D D D D X X U 58 D D X X U U U D DX X U U U 59 D X X U U U U D X X U U U U 60 D X X X X X D X X X X X X U61 D D X X X X U D D X X X X U

Disclosure of the Present Specification

The present specification proposes methods for transmitting andreceiving a reference signal (RS) on a special subframe to supportNarrow band Internet of Things (NB-IoT) employing the Time-DivisionDuplexing (TDD) scheme.

NB-IoT may operate in one of the following three operation modes. Thethree operation modes may include a guard-band operation mode,stand-alone operation mode, and in-band operation mode. After settingthe operation mode, the base station transmits an upper layer signalthrough, for example, a Master Information Block (MIB) or a SystemInformation Block (SIB) to a UE (for example, an NB-IoT device).

The in-band operation mode refers to a mode where an NB-IoT celloperates in part of a band in which a first LTE cell operates. Thein-band operation mode is further divided into an in-band same PCI mode(inband-same PCI) where the NB-IoT cell and the LTE cell share the samephysical cell ID (hereinafter, it is also called a PCI) and an in-banddifferent PCI mode (inband-DifferentPCI) where the NB-IoT cell and theLTE cell use different PCIs.

In the in-band same PCI mode, the number of NRSs is the same as thenumber of CRSs.

The guard-band operation mode refers to a mode where part of the LTEband is designated as a guard band, and the NB-IoT cell uses the guardband not used by the LTE cell. For example, the NB-IoT cell may operateone a guard band existing between a first band where a first LTE celloperates and a second band where a second LTE cell operates.

The stand-alone operation mode refers to a mode where the NB-IoT celloperates on a band where a non-LTE cell operates. For example, theNB-IoT cell may operate in part of a band where a GSM cell operates.

In what follows, for the convenience of descriptions, methods fortransmitting an RS on a special subframe in the NB-IoT will be mostlydescribed; however, it should be noted that the proposed methods may beapplied to general communication systems in the same manner.

I. First Disclosure: Transmission of a Narrowband Reference Signal (NRS)on a Special Subframe

First, except for the case where the operation mode of NB-IoT is thein-band same PCI mode (inband-same PCI), an NB-IoT device (or UE) isunable to use a CRS. Also, the more the number of available downlinkreference signals, the better the accuracy of measurement performed byan NB-IoT device (or UE) and the performance of channel estimationbecome. However, since NB-IoT has been designed by considering only theFDD scheme of the 3GPP release-14 and does not take into account thestructure of a TDD special subframe, NRS transmission based on the TDDscheme may not be easily performed if the existing definition is reused.More specifically, in the case of NB-IoT, a CRS is not used, but an NRSis utilized for improving measurement accuracy and performing channelestimation. The NRS has been designed by using the FDD scheme since therelease-14. However, a method for transmitting an NRS on a TDD specialsubframe has not been studied yet. To this regard, the first disclosureof the present specification proposes a method for transmitting an RSwhich may be used by an NB-IoT device (or UE) on a special subframe.More specifically, the corresponding RS may become an NRS in the NB-IoTcommunication. The methods proposed below may be used separately, or inthe form of a combination of one or more of the methods.

I-1. Method for Transmitting NRS on Third Symbol of Special Subframe

The present section proposes a method for transmitting an NRS by using athird symbol of a special subframe. The third symbol refers to a symbolappearing thirdly on the special subframe.

FIG. 9 illustrates a third symbol of a special subframe described inSection I-1.

The example of FIG. 9 assumes a situation of TDD UL-DL configuration #0and special subframe configuration #0. However, the definition of thethird symbol may be applied to other TDD UL-DL configuration #0 in thesame manner.

A specific example to which the proposal above is applied may bedescribed as follows.

I-1-1. Application Method May be Determined According to SpecialSubframe Configuration Index

I-1-1-1. When a specific special subframe configuration is used, an NRSmay be transmitted to all of the special subframes from the entirecarriers available for NB-IoT.

The aforementioned specific special subframe configuration maycorrespond to #0 and #5 of Table 2.

The aforementioned specific special subframe configuration may bedefined by a special subframe configuration where the length of DwPTS isless than X symbols.

At this time, it is possible that X=3.

The available carrier described above may include an anchor carrier fromwhich an NB-IoT device (or UE) acquires synchronization and also includea non-anchor carrier configured through higher layer signaling.

If information related to special subframe configuration may bedistinguished in a step for acquiring an NPSS and an NSSS, and thedistinguished information may be used for determining whether an NRS isalways transmitted from a third symbol of the special subframe,

The NB-IoT device (namely, UE) may use the NRS of the third symbol ofthe special subframe during a cell selection process.

The NB-IoT device (namely, UE) may use the NRS of the third symbol ofthe special subframe for decoding of an NPBCH.

I-1-1-2. When specific special subframe configuration is used, and thespecial subframe among carriers available for NB-IoT is designated as avalid subframe, an NRS may be transmitted.

The aforementioned specific special subframe configuration maycorrespond to #1, #2, #3, #4, #6, #7, #8, and #9 of Table 2.

Option a. The aforementioned valid subframe is defined as a subframe towhich an NB-IoT device (or UE) expects an NPDCCH or NPDSCH to betransmitted. This information may be delivered to an NB-IoT device (orUE) through higher layer signaling such as one using an SIB or an RRCsignal.

Option b. The aforementioned valid subframe may be an independentmeaning defined only for a special subframe. In this case, the validsubframe with respect to the special frame may be defined as a subframeto which an NRS is transmitted irrespective of transmission of an NPDCCHor an NPDSCH. This information may be delivered to an NB-IoT device (orUE) through higher layer signaling such as one using an SIB or an RRCsignal.

In the case of a special subframe except for the valid subframedelivered through higher layer signaling, information about the specialsubframe to be transmitted dynamically by an NRS through DCI may bedelivered to an NB-IoT device (or UE).

When the information is delivered dynamically through DCI, the deliverymay be applied in conjunction with the option a or option b.

The aforementioned available carrier may include an anchor carrier fromwhich an NB-IoT device (or UE) acquires synchronization also include anon-anchor carrier configured through higher layer signaling.

I-1-1-3. When specific special subframe configuration is used,transmission of an NRS may be determined according to whether totransmit NPDCCH or NPDSCH.

The aforementioned specific special subframe configuration maycorrespond to #9 of Table 2.

For example, when an NPDCCH or an NPDSCH is used, an NRS may be made notto be transmitted to the corresponding special subframe.

Whether an NPDCCH or an NPDSCH is transmitted from the special subframemay be delivered through higher layer signaling such as one using an SIBor an RRC signal or through DCI.

At this time, the SIB, RRC signal, or DCI may include an informationfield of 1-bit length which indicates whether to use a special subframefor data transmission or NRS transmission or may include an informationfield in the form of a bitmap.

As in the proposed method, the reason why the application id determinedaccording to the special subframe configuration index is thatavailability of the third symbol of the special subframe is changedaccording to the special subframe configuration. For example, in thecase of special subframe configuration #0 and #5, the third symbol ofthe special subframe is not used in the legacy LTE system except forcentral six RBs, the special subframe is always available for an NB-IoTcarrier. Meanwhile, in the case of special subframe configuration #1,#2, #3, #4, #6, #7, #8, and #9, the special frame may be used as an LTEPDSCH; therefore, information about whether the corresponding specialsubframe is available in the NB-IoT communication has to be provided.

I-1-2. Application Method May be Determined According to Operation Modeof NB-IoT

1-1-2-1. When the operation mode is in-band, an NRS may be transmittedonly when a specific condition is satisfied.

At this time, the specific condition is a condition for a specialsubframe configuration index.

The specific condition may be a condition about whether the specialsubframe is a valid subframe.

The specific condition may be related to whether the carrier is ananchor carrier and/or a carrier to which an SIB for NB-IoT (for example,SIB1-NB) is transmitted.

At this time, the NB-IoT device (or UE) may assume that an NRS is alwaystransmitted in a DwPTS of the corresponding carrier.

I-1-2-2. When operation mode is guardband or standalone, NRS may bealways transmitted.

After checking the operation mode, an NB-IoT device (or UE) notices thatan NRS always exists in the third symbol of a DwPTS and uses the factfor decoding.

To this end, all of the special subframe configurations include NRStransmission in the third symbol.

For example, it may be configured so that the 3rd, 6th, 7th, and 10thOFDM symbols are used for NRS transmission in the special subframe, andan NRS is transmitted at the corresponding positions when the DwPTSlength includes the OFDM symbol index.

The reason why the application is determined according to the operationmode as in the proposed method is that when the operation mode isguardband or standalone, the DwPTS area may be used only for the purposeof NB-IoT communication. On the other hand, when the operation mode isinband, except for a specific situation, it is not possible to determinewhether a special subframe area is used only for the purpose of NB-IoTcommunication, use of inband mode may be restricted. If the proposedmethod is used, a UE is able to utilize more NRSs in a situation whereonly a limited amount of NRSs is allowed to be used, such as theSIB1-NB, and therefore, performance improvement may be obtained.

I-1-3. NRS Used in the Third Symbol of Special Subframe May Use theFollowing Options.

Option a. A method for generating an NRS used by other downlink subframeand a method for determining frequency domain resources may be used.

A method for generating a sequence of the NRS may reuse an existingmethod for generating an NRS sequence according to Eqs. 1 to 3.

The position of a frequency domain resource of the NRS may be determinedby the k value which determines a mapping position in the frequencydomain of the method defined by Eq. 1.

At this time, the position of the time domain resource to be applied maybe determined so that 1=2 at the first slot. This position correspondsto the third symbol of the special subframe. An embodiment thereof isillustrated in FIG. 10.

Option b. The option b may determine to use a method for generating anNRS newly defined for the third symbol of a special subframe and afrequency domain mapping rule. At this time, the newly defined NRS maybe designed to use all of 12 resource elements (REs) used by the thirdsymbol.

As one example, a Zadoff-Chu sequence may be used. At this time, theroot index of the Zadoff-Chu sequence may be determined by NNcellIDwhich distinguishes an NB-IoT cell ID.

For example, a Gold sequence may be used. At this time, the C_(init)value of the Gold sequence may be determined by NNcellID whichdistinguishes an NB-IoT cell ID.

This method may be applied only to the case where the corresponding NRSsymbol is not used for the purpose of data transmission. To this end, abase station may deliver information about whether a newly defined NRSis transmitted to the corresponding position to an NB-IoT device (or UE)through higher layer signal or DCI.

The option a described above provides an advantage that an existingmethod may be reused. The option b may be intended to lower PAPR byusing all of the REs when data are not transmitted to the correspondingsymbol.

I-1-4. Energy per resource element (EPRE) of NRS transmitted from thethird symbol of special subframe may be configured separately from theEPRE of NRS transmitted from a different subframe.

I-1-4-1. The EPRE of an NRS transmitted from the third symbol of aspecial subframe may be determined by an offset (or in the form of amultiple) from the EPRE of an NRS transmitted from a different subframe.

Option a. At this time, the EPRE of an NRS transmitted from the thirdsymbol of a special subframe may be delivered to an NB-IoT device (orUE) through higher layer signaling using an SIB or an RRC signal.

At this time, the EPRE of an NRS transmitted from the third symbol ofthe special subframe may be determined by a fixed offset from the EPREof an NRS transmitted from a different subframe.

The option above may be applied only for the case where data are notmapped to the third symbol of the special subframe.

For example, when the number of REs to which an NRS from the thirdsymbol of the special subframe is mapped is N, and the EPRE of an NRSfrom a different DL subframe is defined by ENRS, the EPRE of the NRSused at the third symbol of the special subframe may be defined by themathematical equation below.

$\begin{matrix}{E_{{NRS}\_ {special}} = {E_{NRS} \times \frac{12}{N}}} & \left\lbrack {{Eq}.\mspace{14mu} 4} \right\rbrack\end{matrix}$

I-2. Method for Transmitting NRS by Using First to Third Symbols ofSpecial Subframe

The method proposed in the present section includes a method fortransmitting an NRS using a first to third symbols of a specialsubframe. At this time, the first to the third symbols indicate thesymbols appearing firstly, secondly, and thirdly on the specialsubframe, respectively.

FIG. 11 illustrates a symbol to which an NRS is mapped according toSection I-2.

The embodiment of FIG. 11 assumes a situation based on UL-DLconfiguration #0 and special subframe configuration #0, but it should beclearly understood that the definition of the first, second, and thirdsymbols may be applied in the same way for other TDD configurations.

The proposed method is a special case of the method described in SectionI-1, and the operations other than those given in the descriptions belowmay be performed in the same manner as in the method described inSection I-1. For example, a method for distinguishing a special subframeconfiguration index or a method for configuring the EPRE for which thecorresponding method is applied may be applied in the same manner as inthe method described in Section I-1.

A specific method to which the proposed specification is applied may bedescribed as follows.

The proposed specification may be applied only to the case where theoperation mode of the corresponding cell is the guard band orstand-alone.

If the operation mode is in-band, an NB-IoT device (or UE) may assumethat an NRS is transmitted according to a criterion described in SectionI-1.

If the NB-IoT device (or UE) has not obtained information about theoperation mode of the corresponding cell yet, it may be assumed that theNRS is transmitted according to the criterion described in Section I-1.

The reason why the operation mode determines whether to use the methodas described above is that in the case of the guard band operation modeand the stand-alone mode, the control region used for the legacy LTEsystem is not configured, and thus the first and second symbols may beused additionally. Also, since an NRS is transmitted by using a largernumber of symbols, an advantage is obtained that the number of REs whichmay be used for an NB-IoT device (or UE) to perform channel measurementor estimation is increased.

I-2-1. NRS used in the first, second, and third symbols of specialsubframe may be as follows.

Option a. The option a may determine to use a method for generating anNRS used in a different downlink subframe and a method for determiningfrequency domain resources.

A method for generating a sequence of the NRS may reuse an existingmethod for generating an NRS sequence according to Eqs. 1 to 3.

The position of the NRS in the frequency domain may be determined by thek value which determines a mapping position in the frequency domainaccording to the method defined by Eq. 1.

At this time, the position of an applied time domain resource may bedetermined as follows.

-   -   In the first slot, 1=0, 1. This corresponds to the position        indicating the first and the second symbol of a special        subframe.    -   In the first slot, 1=1, 2. This corresponds to the position        indicating the second and the third symbol of the special        subframe.    -   In the first slot, 1=0, 1, 2.

At this time, when 1=0, 1, it may be determined to use an existingmethod for generating an NRS according to Eqs. 1 to 3.

At this time, when 1=2, it may be determined to use a method forgenerating an NRS mapped to the third symbol in Section I-1.

Option b. The option b may determine to use a method for generating anNRS newly defined for the first, second, and third symbols of a specialsubframe and a frequency domain mapping rule.

At this time, the newly defined NRS may be designed to form a sequenceof length 12 with reference to 12 resource elements (REs) used by onesymbol.

A sequence generated with reference to one symbol may be mappedrepeatedly onto three symbols used for NRS transmission in a specialsubframe. At this time, a cover code which is intended fordistinguishing an antenna port or cell ID may be applied to each symbol.

At this time, the cover code applied to the third symbol may bedetermined to have a value of 1.

As one example of a sequence mapped to one symbol, the Zadoff-Chusequence may be used. At this time, the root index of the Zadoff-Chusequence may be determined by NNcellID which distinguishes an NB-IoTcell ID.

As one example of a sequence mapped to one symbol, a Gold sequence maybe used. At this time, the C_(init) value of the Gold sequence may bedetermined by NNcellID which distinguishes an NB-IoT cell ID.

The option a is advantageous in that an existing method may be reused.When a method with a condition of 1=0, 1, 2 of the option a is usedtogether, an advantage is obtained that even when an NB-IoT device (orUE) does not know the operation mode, the NRS of the third symbol may beestimated based on the method with a condition of 1-1. A method based onthe option b may be aimed to lower PAPR by using all of the REs whendata are not transmitted to the corresponding symbol. At this time, amethod for generating an NRS of the third symbol and a method forapplying a cover code may be intended for the NRS of the third symbol tobe used even when an NB-IoT device (or UE) does not know the operationmode.

I-3. Method for Transmitting NRS by Using the Sixth and Seventh Symbolsof Special Subframe

The present section proposes a method for transmitting an NRS by usingthe sixth and seventh symbols of a special subframe. At this time, thesixth and the seventh symbol refer to the symbols appearing sixth andseventh on the special subframe, respectively.

FIG. 12 illustrates a symbol to which an NRS is mapped according toSection I-3.

The embodiment of FIG. 12 assumes a situation based on UL-DLconfiguration #0 and special subframe configuration #1, but an NRS mayalso be transmitted on the sixth and seventh symbols for the case of adifferent TDD configuration.

A specific method to which the proposed specification is applied may bedescribed as follows.

I-3-1. Application Method May be Determined According to SpecialSubframe Configuration Index

I-3-1-1. When a specific special subframe configuration is used, theproposed method may not be applied.

The aforementioned specific special subframe configuration maycorrespond to #0 and #5 of Table 2.

The aforementioned specific special subframe configuration may bedefined by a special subframe configuration where the length of DwPTS isless than X symbols.

At this time, it is possible that X=3.

I-3-1-2. When a specific special subframe configuration is used, and thespecial subframe among carriers available for NB-IoT is designated as avalid subframe, an NRS may be transmitted.

The aforementioned specific special subframe configuration maycorrespond to #1, #2, #3, #4, #6, #7, #8, and #9 of Table 2.

Option a. The aforementioned valid subframe is defined as a subframe towhich an NB-IoT device (or UE) expects an NPDCCH or NPDSCH to betransmitted. This information may be delivered to an NB-IoT device (orUE) through higher layer signaling such as one using an SIB or an RRCsignal.

Option b. The aforementioned valid subframe may be an independentmeaning defined only for a special subframe. In this case, the validsubframe with respect to the special frame may be defined as a subframeto which an NRS is transmitted irrespective of transmission of an NPDCCHor an NPDSCH. This information may be delivered to an NB-IoT device (orUE) through higher layer signaling such as one using an SIB or an RRCsignal.

In the case of a special subframe except for the valid subframedelivered through higher layer signaling, information about the specialsubframe to be transmitted dynamically by an NRS through DCI may bedelivered to an NB-IoT device.

When the information is delivered dynamically through DCI, the deliverymay be applied in conjunction with the option a or option b.

The aforementioned available carrier may include an anchor carrier fromwhich an NB-IoT device (or UE) acquires synchronization also include anon-anchor carrier configured through higher layer signaling.

More specifically, in the case of special subframe configuration #9, itis proposed as follows.

-   -   It may be determined that only the sixth symbol is used for NRS        transmission. This may be intended to guard a DwPTS slot        available for the special subframe configuration #9.    -   Both of the sixth and seventh symbols may be used for NRS        transmission. This may be intended to increase transmission of        the NRS when there is no significant difficulty in securing GAP.

The base station may determine whether to transmit an NRS to the seventhsymbol, and this information may be delivered to an NB-IoT device (orUE) through higher layer signaling using an SIB or an RRS signal.

In the method described above, the cases of special subframeconfiguration #0 and #5 may be excluded from application since the sixthand seventh symbols of the special subframe are not configured to be inthe DwPTS region. On the other hand, since the special subframe may beused as the LTE PDSCH in the cases of special subframe configuration #1,#2, #3, #4, #6, #7, #8, and #9, information about whether thecorresponding special subframe is available for NB-IoT has to beprovided.

I-3-1-3. When an NRS is transmitted from the sixth and seventh symbolsof a special subframe, it may be proposed as follows.

A method for generating an NRS used in a different downlink subframe anda method for determining a time-frequency domain resource may determineto use a resource corresponding to a first slot.

If a special subframe configuration #9 is used, and only the sixthsymbol is used for NRS transmission, a time resource to be used may bedetermined only for the case where 1=5.

I-3-1-4. Energy per resource element (EPRE) of an NRS transmitted fromthe sixth and seventh symbols of a special subframe may be configuredseparately from the EPRE of an NRS transmitted from a differentsubframe.

At this time, the EPRE of an NRS transmitted from the special subframemay be determined by an offset (or in the form of a multiple) from theEPRE of an NRS transmitted from a different subframe.

At this time, the EPRE of an NRS transmitted from the special subframemay be delivered to an NB-IoT device (or UE) through higher layersignaling using an SIB or an RRC signal.

The case where the EPRE of an NRS transmitted from a different subframeis applied differently may be limited to the case where an NPDCCH orNPDSCH is not transmitted to the corresponding special subframe.

At this time, the base station may deliver information about whether thecorresponding special subframe is to be used as an NPDCCH or NPDSCHthrough higher layer signaling using an SIB or an RRC signal.

II. Second Disclosure: Uplink Reference Signal in a Special Subframe

In the TDD scheme, the uplink transmission region of a special subframeis limited to UpPTS region. In general, the UpPTS is determined to havea symbol length of 1 or 2. A legacy LTE UE may use the region for thepurpose of an SRS or a PRACH. In the case of NB-IoT, since the minimumunit for NPUSCH transmission is fixed as a slot, the UpPTS of a specialsubframe may not be appropriate for data transmission. Also, whenintervals among groups of symbols used as transmission units for NPRACHtransmission and hopping among the symbol groups are considered, theUpPTS may not be appropriate for transmission of the NPRACH. Also, theNB-IoT technology of up to release 14 does not define an operation fortransmitting an SRS.

To this regard, the present invention proposes a method to be used fortransmitting an uplink reference signal. More specifically, the proposedmethod for transmitting an uplink reference signal, when used forNB-IoT, may have the form and purpose as an SRS is transmitted. Themethods described below may be used independently of each other or inthe form of a combination of one or more methods.

II-1. Method for Configuring to Transmit an SRS Only for a Valid SpecialSubframe

A method proposed by the present specification may be determined tooperate only for a case where a special subframe is configured as avalid subframe. At this time, a valid subframe refers to a subframeconfigured by a base station, which allows an NB-IoT device (or UE) toperform uplink transmission. At this time, a valid subframe for an SRSworks as information to indicate whether each special subframe isallowed for uplink transmission, which may be provided independently.This information may be informed to an NB-IoT device (or UE) throughhigher layer signal using an SIB or an RRC signal. If aperiodic SRStransmission is configured by using an NPDCCH, information about a validsubframe may be configured dynamically by using a predetermined area ofDCI.

II-2. Method for Transmitting an SRS to One or More Carriers by UsingCarrier Hopping

Since NB-IoT is designed to operate using one carrier (morespecifically, one PRB comprising 12 subcarriers), it may beinappropriate to transmit an SRS to a plurality of carrierssimultaneously. Therefore, when a plurality of carriers (namely anchorcarrier and a plurality of non-anchor carriers) are available, a methodfor transmitting an SRS is needed for carriers to which an SRS may betransmitted. A method proposed in the present section may include amethod for hopping carriers to which an SRS is transmitted to perform anSRS operation on a plurality of carriers.

Carrier hopping may be performed on an anchor carrier and/or non-anchorcarriers configured for an NB-IoT device (or UE). At this time, targetcarriers on which carrier hopping is performed may be determined by acombination of one or more options given below.

Option a. Carrier hopping is determined to be performed on the carriersconfigured by an SIB so that an NB-IoT device (or UE) may perform pagingor NPRACH.

Option b. Carrier hopping may be performed on the carriers configuredseparately through higher layer signaling using an SIB or an RRC signal.

Option c. Carrier hopping may be performed on the carriers configuredseparately through DCI.

Carrier hopping may not be performed while repeated transmission isperformed. When the number of repetitions that an NB-IoT device (or UE)has to perform for each carrier to support coverage is predetermined,carrier hopping may be determined not to be performed while thecorresponding repetitions are being performed.

A carrier hopping pattern may be determined to have different patternsfor each cell. This may be intended to reduce inter-cell interference.

II-3. Method for Transmitting a Periodic SRS of an NB-IoT

An NB-IoT device (or UE) may transmit an SRS periodically. To thispurpose, a base station may deliver necessary information through higherlayer signaling using an SIB or an RRC signal. The necessary informationdescribed above may include one or more of the information given below.

-   -   Period: A period for transmitting an SRS may be specified. At        this time, the period may be defined as an interval between        positions at which SRS transmission is started. If SRS        transmission is impossible because the start position of SRS        transmission specified by a period corresponds to an invalid        subframe, SRS transmission may be given up on the corresponding        UpPTS.    -   Time offset: Information of a time offset may be used for        determining the position for transmitting an SRS for the first        time. For example, the time offset may be determined so that the        initial SRS transmission is performed after a configured time        offset measured from the moment CDRX is completed. If SRS        transmission is impossible because the start position of SRS        transmission specified through the time offset corresponds to an        invalid subframe, SRS transmission may be given up on the        corresponding UpPTS. If the period information is applied, a        period value may be applied after the SRS start position        configured by the time offset.    -   Starting carrier: A carrier from which SRS transmission is        started may be determined. After the starting carrier performs        SRS transmission, a carrier to transmit the SRS may be selected        according to a carrier hopping pattern. At this time, the        starting carrier may be a carrier on which an NB-IoT device (or        UE) camps. Similarly, the starting carrier may always be        determined as an anchor carrier. Or the starting carrier may be        a specific carrier configured through higher layer signaling.    -   Repetition: Transmission of an SRS may be repeated on one or        more UpPTSs. This may be intended to obtain sufficient power        required for SRS transmission.

II-4. Method for Transmitting an Aperiodic SRS of an NB-IoT Device

An NB-IoT device (or UE) may transmit an SRS aperiodically. To this end,a base station may deliver necessary common information to the NB-IoTdevice (or UE) through higher layer signaling using an SIB or an RRCsignal, and part of individual information may be configured throughDCI. If a periodic SRS is configured, part of the necessary commoninformation above may be utilized for transmission of a periodic SRS.The necessary individual information described above may include one ormore information defined in Section II-3.

II-5. Method for Determining Repetition According to the Number ofSymbols Comprising UpPTS

If the number of OFDM symbols available for an UpPTS is larger than 2,an NB-IoT device (or UE) may transmit an SRS repeatedly. At this time,the number of repetitions may be the same as the number of OFDM symbolsavailable in the UpPTS.

When repetition is applied, OFDM symbols belonging to one UpPTS (ormultiple UpPTSs) are regarded as belonging to one group, and a covercode in units of OFDM symbols may be applied. This may be intended formultiplexing a plurality of NB-IoT devices (or UEs) within the same cellor for reducing inter-cell interference. At this time, each NB-IoTdevice (or UE) may determine the cover code type to be used by itselfbased on its ID (namely UE ID) or information configured by the basestation. The information may be configured through higher layersignaling using an SIB or an RRC signal; or configured dynamicallythrough DCI when aperiodic SRS transmission is configured by the NPDCCH.

II-6. Method for Resolving Collision with Other Channel Having DifferentSRS Transmission Timing

If an NB-IoT device (or UE) detects DCI corresponding to a downlinkgrant, an SRS may not be transmitted for a duration since an NPDSCH isreceived until ACK/NACK is transmitted in response thereto. Also, if anNB-IoT device (or UE) detects DCI corresponding to an uplink grant, anSRS may not be transmitted while NPUSCH transmission is performed. Thismay be intended to reduce time required for frequency retuning and powerconsumption.

A downlink SRS gap may be configured for a predetermined time periodafter transmission of an NPUSCH (data and/or ACK/NACK), which determinesnot to transmit an SRS. This may be intended to guarantee the case wherereception of an NPDSCH or transmission of an NPUSCH is performedcontinuously through the next DCI.

When a resource for an NPRACH or a scheduling request is configured, anSRS may be determined not to be transmitted for the case of an UpPTSlocated right before the uplink subframe for which the correspondingresource is configured. This is intended to secure time for frequencyretuning of an NB-IoT device (or UE).

II-7. Method for Specifying Subcarrier Allocation

In NB-IoT uplink transmission, uplink transmission using 1, 3, 6, and 12subcarriers is possible. At this time, an NB-IoT device (or UE) may becapable of supporting only one carrier. Taking into account thisfeature, the present section may include a method for distinguishing SRStransmission using 1, 3, 6, and 12 subcarriers.

II-7-1. When SRS transmission using one or more subcarriers is allowed,SRS transmission methods corresponding to the respective numbers ofsubcarriers may differ from each other.

At this time, the size of a subcarrier which transmits an SRS may bedifferent from each other in terms of SRS transmission units comprisingthe subcarrier in the time domain.

For example, when an SRS is transmitted using 1, 3, 6, and 12subcarriers, X1, X2, X3, or X4 UpPTS regions may be used as one SRSunit, respectively.

When an SRS is transmitted by using one subcarrier, a sequence may becomposed in X1 UpPTS regions of the time domain. This may be intended toidentify different NB-IoT devices (or UEs) within the same cell orreduce inter-cell interference.

II-7-2. When an SRS is transmitted by using one or more subcarriers, SRSresources which transmits the SRS may be configured separately accordingto the number of subcarrier used.

At this time, one UpPTS symbol may be configured such that its resourceson the frequency domain are distinguished in the FDM form to support SRStransmission using 1, 3, and 6 subcarriers.

At this time, a specific UpPTS may be used for supporting an SRS whichuses a specific subcarrier number.

At this time, information about SRS resources used may be delivered toan NB-IoT device (or UE) through higher layer signaling using an SIB oran RRC signal according to the size of each subcarrier.

At this time, if SRS transmission is performed aperiodically using anNPDCCH, the number of subcarriers to be selected by the NB-IoT device(or UE) and information about SRS resources may be delivered dynamicallythrough DCI.

III. Third Disclosure: RS Configuration for Special SubframeConfiguration #10

According to the definition of frame structure type 2, the total numberof special subframe configurations available for the TDD structure is11. In particular, the special subframe configuration #10, which is anew structure introduced since the release-14, uses 6 OFDM symbols inthe DwPTS region and 6 OFDM symbols in the UpPTS region as a new CPcriterion. More specifically, the special subframe configuration #10 maydetermine whether to transmit a CRS to the fifth symbol position of theDwPTS region. If the base station supports the special subframeconfiguration #10 for which CRS-less DwPTS has been configured, legacyLTE UEs are unable to expect a CRS at the fifth OFDM symbol of the DwPTSregion from the corresponding base station. A primary reason of theaforementioned structure is to minimize interference imposed on ULtransmission by the DwPTS region.

In what follows, when the subframe configuration #10 is used for theNB-IoT TDD structure, RSs are used independently from each other. Themethods proposed below may be used separately or in the form of acombination thereof. In what follows, unless described specifically,descriptions below are related to the methods for RS transmission withrespect to the fifth OFDM symbol of the DwPTS region.

III-1. Method for Transmitting an RS to the Fifth Symbol of SpecialSubframe Configuration #10

The method proposed by the present section enables a base station totransmit an RS to the position of the fifth symbol of a DwPTS when thespecial subframe configuration #10 is configured and an NB-IoT device toreceive and use the RS. In general, an RS may be used for the purposesof channel estimation and measurement and provide higher accuracy as theRS density becomes higher (namely the more the RSs become available).

Detailed descriptions of the proposed method may be as follows.

III-1-1. The proposed method may be applied when the operation mode ofan NB-IoT is the in-band mode.

When the operation mode of an NB-IoT is the in-band same PCI mode, theRS transmitted may be a CRS.

At this time, the transmitted CRS may be determined to follow the CRSpattern and generation rule of the fifth OFDM symbol of a downlinksubframe.

When the operation mode of an NB-IoT is in-ban different PCI(inband-DifferentPCI) mode, the RS transmitted may be an NRS.

At this time, the transmitted NRS may follow one of the patterns andgeneration rules among OFDM symbols (for example, the sixth and seventhsymbols in a slot) including the NRS in the downlink subframe.

At this time, the pattern to be selected and the generation rule may bedetermined based on the sixth OFDM symbol when the index of a specialsubframe is an odd number and the seventh OFDM symbol when the index isan even number (or vice versa).

The reason for determining whether to transmit an RS according to theoperation mode as described above is that when the operation mode is theguardband or standalone mode, there may be no influence by a CRS-lessDwPTS. Also, when the operation mode is the in-band same PCI mode, anNB-IoT device, being aware of the information about the CRS pattern andthe generation rule, may perform decoding by using the information.Also, the reason is that when the operation mode is the in-band same PCImode, the NB-IoT device becomes able to transmit a CRS so thatcross-subframe channel estimation or symbol-level combining may beapplied easily. Also, when the operation mode is the inband-DifferentPCImode, since an NB-IoT device does not know the CRS pattern and thegeneration rule, it regards the position of the CRS as an RE which isnot used normally. However, if the CRS-less DwPTS is configured, it maybe expected that an RS is not transmitted to the transmission positionof the CRS at the fifth symbol of the DwPTS. Therefore, in this case, itmay be determined that the position of the corresponding CRS is used formapping of an NRS which may be recognized by an NB-IoT device.

III-1-2. The proposed method may be applied to the case where a DwPTSregion is configured as a valid subframe.

If a specific DwPTS is invalid, an NB-IoT device does not expect an RSto be transmitted at the fifth OFDM symbol of the corresponding DwPTS.

The proposed method may be applied only for the case where actual dataare transmitted to the DwPTS region.

The proposed method may be applied only for the case where an NRS isincluded in a different OFDM symbol other than the fifth OFDM symbol inthe DwPTS region.

When an NB-IoT device does not know whether an NRS is included in adifferent OFDM symbol other than the fifth OFDM symbol in a specificDwPTS region, the corresponding NB-IoT device does not expect a CRS tobe transmitted in the corresponding DwPTS region.

The reason why the proposed method allows RS transmission on a validsubframe is that when a base station declares the corresponding DwPTSregion as valid, the corresponding DwPTS region may be regarded as beingallowed to be used for the purpose of NB-IoT. Also, even when the basestation declares a specific DwPTS as valid, if actual data or an NRS isnot transmitted to the specific DwPTS, the base station may be regardedto intend to avoid interference due to uplink transmission by skippingtransmission in the corresponding DwPTS.

III-1-3. The proposed method may be applied when transmission of anNPDSCH granted through an NPDCCH is scheduled so that transmission at aDwPTS may be performed.

At this time, the NPDCCH may be determined not to be transmitted throughthe DwPTS.

At this time, whether NPDSCH transmission is allowed at the DwPTS may bedelivered to a UE through information included in the DCI obtainedthrough the NPDCCH. For example, the information may include DCI bit,CRC masking value, and so on.

At this time, whether NPDSCH transmission is allowed at the DwPTS may bedetermined according to the transmission length of the NPDSCH deliveredby the DCI.

The transmission length may refer to the repetition size of the NPDSCH,the number of downlink subframes required to map one TB to an RE, or acombination of both. More specifically, whether NPDSCH transmission isallowed at the DwPTS may be determined for the case where thetransmission length is less than M subframes with respect to a specificconstant M. Or whether NPDSCH transmission is allowed at the DwPTS maybe determined for the case where the number of DwPTSs involved intransmission of the NPDSCH is less than N with respect to a specificconstant N.

According to the method described above, an advantage is obtained that abase station may dynamically control transmission of the NPDSCH at theDwPTS depending on the situation. Also, when the number of DwPTSs usedfor transmission of the NPDSCH is small since the length of NPDSCHtransmission is short, transmission of the corresponding NPDSCH exertsrelatively little influence, and therefore, in this case, thetransmission may be allowed.

III-1-4. The proposed method may be determined to be always applied forthe anchor carrier.

At this time, transmission may be determined only by higher layersignaling.

In the case of an anchor carrier, since NPSS/NSSS is transmittedperiodically, the number of subframes capable of transmitting an NRS maybe relatively small compared with a non-anchor carrier. Also, the moresubframes to which an CRS and an NRS are transmitted, the moreadvantageous to improve decoding performance of SIB1-NB. Also, since ananchor carrier may be regarded as a subframe allocated by the basestation for NB-IoT, a probability that downlink/uplink transmission forother purposes occurs may be relatively low. Therefore, an in theproposed method, it may be advantageous to always expect an RS in theDwPTS region of the anchor carrier.

III-1-5. The proposed method may be applied when NPRACH transmission isstarted within K subframes after DwPTS.

At this time, the K value may be a predefined value.

The proposed method may be applied to a carrier capable of performingRRM measurement before a UE performs NPRACH.

The carrier may be determined as an anchor carrier.

The carrier may be determined as a carrier from which an NB-IoT deviceexpects to receive the second message (Msg2) (namely, random accessresponse) and/or fourth message (Msg4) of a random access procedure.

An NB-IoT device needs to know its CE level accurately Before performingthe random access procedure (namely NPRACH). The NB-IoT device mayperform RRM measurement using an RS to measure the CE level, and theproposed method may be intended to allow the UE to secure more RSs toestimate the CE level under such a situation.

III-2. Method for not Transmitting an RS to the Fifth Symbol of SpecialSubframe Configuration #10

According to the proposed method in this section, a base station doesnot transmit an RS to the position of the fifth symbol of a DwPTS, whichmay be recognized by an NB-IoT; and the RS at the corresponding positionmay be made not to be used.

A specific example to which the proposed method is applied may be asfollows.

III-2-1. When actual data transmission is performed in the DwPTS region,all of the REs of the fifth OFDM symbol of the corresponding DwPTS maybe used for the purpose of data transmission.

In some cases, instead of increasing the density of RS, securing asufficient number of REs for data and lowering the code rate may be moreadvantageous. Similarly, in terms of complexity of a UE, instead ofapplying an RS differently according to the situation, it may be moreadvantageous to always assume that an RS is not available.

The embodiments of the present invention described above may beimplemented through various means. For example, embodiments of thepresent invention may be implemented by hardware, firmware, software, ora combination thereof. More specifically, implementation of theembodiments will be described with reference to related drawings.

FIG. 13 illustrates a block diagram of a wireless device and a basestation in which a disclosure of the present specification isimplemented.

Referring to FIG. 13, a wireless device 100 and a base station 200 mayimplement the disclosure of the present specification.

The wireless device 100 in the figure comprises a processor 101, memory102, and transceiver 103. In the same manner, the base station 200comprises a processor 201, memory 202, and transceiver 203. Theprocessor 101, 201, memory 102, 202, and transceiver 103, 203 may beimplemented by the respective chips, or at least two or moreblocks/functions may be implemented through one chip.

The transceiver 103, 203 includes a transmitter and a receiver. When aspecific operation is performed, an operation of only one of thetransmitter and the receiver may be performed, or both of thetransmitter and receiver operations may be performed. The transceiver103, 203 may include one or more antennas transmitting and/or receivinga radio signal. Also, the transceiver 103, 203 may include an amplifierfor amplifying a reception signal and/or transmission signal; and abandpass filter for transmission to a specific frequency band.

The processor 101, 201 may implement functions, processes and/or methodsproposed by the present specification. The processor 101, 201 mayinclude an encoder and a decoder. For example, the processor 101, 202may perform an operation due to the methods described above. Theprocessor 101, 201 may include application-specific integrated circuit(ASIC), other chipsets, logic circuits, data processing apparatus and/orconverter which converts a baseband signal and a radio signal to eachother.

The memory 102, 202 may include Read-Only Memory (ROM), Random AccessMemory (RAM), flash memory, memory card, storage medium and/or otherstorage devices.

FIG. 14 is a detailed block diagram of a transceiver of a wirelessdevice of FIG. 13.

Referring to FIG. 14, a transceiver 110 comprises a transmitter 111 anda receiver 112. The transmitter 111 comprises a Discrete FourierTransform (DFT) unit 1111, subcarrier mapper 1112, IFFT unit 1113, CPinserting unit 1114, and wireless transmitting unit 1115. Thetransmitter 111 may further comprise a modulator. Also, for example, thetransmitter 111 may further comprise a scramble unit (not shown),modulation mapper (not shown), layer mapper (not shown), and layerpermutator, which may be disposed in from of the DFT unit 1111. In otherwords, to prevent increase of peak-to-average power ratio (PAPR), thetransmitter 111 first makes information go through the DFT 1111 beforemapping a signal to a subcarrier. A signal spread (or precoded in thesame context) by the DFT unit 1111 goes through subcarrier mappingthrough the subcarrier mapper 1112 and is converted again to atime-series signal through the Inverse Fast Fourier Transform (IFFT)unit 1113.

The DFT unit 1111 performs DFT on the input symbols to produce symbolsof complex-number symbols. For example, if Ntx symbols are input (whereNtx is a natural number), its DFT size is Ntx. The DFT unit 1111 may becalled a transform precoder. The subcarrier mapper 1112 maps thecomplex-number symbols to the respective subcarriers in the frequencydomain. The complex-number symbols may be mapped to resource elementscorresponding to a resource block allocated for data transmission. Thesubcarrier mapper 1112 may be called a resource element mapper. IFFTunit 1113 performs IFFT on the input symbols to produce a basebandsignal for data, which is a signal in the time domain. The CP insertingunit 1114 copies part of the trailing portion of the baseband signal fordata and inserts the part into the leading portion of the basebandsignal for data. Through CP insertion, inter-symbol interference (ISI)and inter-carrier interference (ICI) may be prevented, and thusorthogonality may be maintained even for multi-path channels.

On the other hand, the receiver 112 may comprise a wireless receivingunit 1121, CP removing unit 1122, FFT unit 1123, and equalizing unit1124. The wireless receiving unit 1121, CP removing unit 1122, and FFTunit 1123 of the receiver 112 perform the inverse roles of the wirelesstransmitting unit 1115, CP inserting unit 1114, and the IFFT unit 1113of the transmitter 111. The receiver 112 may further comprise ademodulator.

What is claimed is:
 1. A method of receiving a narrowband referencesignal (NRS), the method performed by a narrowband internet of things(NB-IoT) device and comprising: determining information regarding a timedivision duplex (TDD) special subframe configuration, among a pluralityof TDD special subframe configurations that each configures a pluralityof downlink (DL) orthogonal frequency division multiplexing (OFDM)symbols and at least one uplink (UL) OFDM symbol within a TDD specialsubframe; and receiving the NRS on at least one DL OFDM symbol among theplurality of DL OFDM symbols within the TDD special subframe, wherein asymbol location of the at least one DL OFDM symbol for receiving the NRSis determined based on the TDD special subframe configuration.
 2. Themethod of claim 1, wherein the TDD special subframe comprising the atleast one DL OFDM symbol for receiving the NRS uses at least one of TDDspecial configuration indexes 1, 2, 3, 4, 6, 7, 8, or
 9. 3. The methodof claim 1, wherein the at least one DL OFDM symbol for receiving theNRS comprises at least one of a 6th symbol or a 7th symbol in the TDDspecial subframe.
 4. The method of claim 1, wherein the NRS is notreceived on at least one TDD special subframe using TDD specialconfiguration indexes 0 and
 5. 5. The method of claim 1, wherein the atleast one DL OFDM symbol for receiving the NRS comprises at least one ofa 2nd symbol or a 3rd symbol in the TDD special subframe.
 6. The methodof claim 1, wherein the NRS on the TDD special subframe is generatedbased on a normal downlink subframe.
 7. The method of claim 1, furthercomprising: receiving a second reference signal (RS) in a second TDDspecial subframe using a TDD special subframe configuration index
 10. 8.The method of claim 7, wherein based on an NB-IoT operation mode beingan inband-same PCI mode representing an inband-same physical cellidentifier (PCI): the second RS comprises a cell-specific referencesignal (CRS).
 9. The method of claim 8, wherein based on the NB-IoToperation mode being the inband-same PCI representing the inband-samePCI: a location of a resource element (RE) to which the NRS is mapped isdifferent from a location of a RE to which the CRS is mapped.
 10. Themethod of claim 8, wherein based on a NB-IoT operation mode being aninband-different PCI mode representing an inband-different PCI: thesecond RS comprises an NRS.
 11. The method of claim 10, wherein based onthe NB-IoT operation mode being the inband-different PCI representingthe inband-different PCI: an RE to which the CRS is to be mapped is usedas a blank RE.
 12. The method of claim 7, wherein the second TDD specialsubframe using the TDD special subframe configuration index 10 isdesignated as a valid subframe.
 13. The method of claim 11, wherein thesecond TDD special subframe using the TDD special subframe configurationindex 10 comprises a downlink pilot time slot (DwPTS) in which adownlink data is to be received.
 14. The method of claim 1, wherein theTDD special subframe in which the NRS is received is a valid subframe inwhich a downlink data is to be received.
 15. The method of claim 1,wherein the TDD special subframe comprises at least three DL OFDMsymbols for receiving the NRS, and uses at least one of TDD specialconfiguration indexes 1, 2, 3, 4, 6, 7, 8, or
 9. 16. The method of claim1, wherein for a first TDD special subframe configuration among theplurality of TDD special subframe configurations, the symbol location ofthe at least one DL OFDM symbol comprises a third symbol in the TDDspecial subframe, and wherein for a second TDD special subframeconfiguration among the plurality of TDD special subframeconfigurations, the symbol location of the at least one DL OFDM symbolcomprises a sixth symbol in the TDD special subframe.
 17. The method ofclaim 1, wherein the TDD special subframe configuration relates to a TDDspecial subframe that comprises a downlink pilot time slot (DwPTS), aguard period (GP), and an uplink pilot time slot (UpPTS).
 18. The methodof claim 1, wherein at least one of a number of DL OFDM symbols or anumber of UL OFDM symbols is different for different TDD specialsubframe configurations among the plurality of TDD special subframeconfigurations.
 19. A narrowband internet of things (NB-IoT) deviceconfigured to receive a narrowband reference signal (NRS), the NB-IoTdevice comprising: a transceiver; at least one processor; and at leastone computer memory operably connectable to the at least one processorand storing instructions that, when executed by the at least oneprocessor, perform operations comprising: determining informationregarding a time division duplex (TDD) special subframe configuration,among a plurality of TDD special subframe configurations that eachconfigures a plurality of downlink (DL) orthogonal frequency divisionmultiplexing (OFDM) symbols and at least one uplink (UL) OFDM symbolwithin a TDD special subframe; and receiving, via the transceiver, theNRS on at least one DL OFDM symbol among the plurality of DL OFDMsymbols within the TDD special subframe, wherein a symbol location ofthe at least one OFDM symbol for receiving the NRS is determined basedon the TDD special subframe configuration.